Ten inbred strains of mice were fed an atherogenic diet containing 1.25% cholesterol, 0.5% cholic acid and 15% fat. The strains were examined for plasma cholesterol and triglyceride levels and for formation of lipid-containing lesions in the aortic wall. The strains differed considerably in the frequency of lesion formation after 14 weeks on the atherogenic diet with a range of 0-1.8 lesions/mouse. The order of susceptibility to lesion formation from the least susceptible to the most susceptible was BALB/cJ, C3H/J, A/J, SWR/J, NZB/J, less than 129/J, AKR/J, DBA/2J, less than C57L/J less than C57BL/6J. Total plasma cholesterol after 5 weeks on the diet varied from 131 mg/dl to 328 mg/dl among strains; however, there was little correlation between total cholesterol levels and susceptibility to lesion formation (r = 0.29). Plasma triglycerides after 5 weeks on the diet varied less than cholesterol with a range of 137-220 mg/dl. An analysis of the genetic differences among inbred strains of mice might provide useful insights into lipid metabolism and the development of atherosclerosis.